Early agricultural harvesters had only an internal combustion engine to cool. To keep the radiator from plugging, an air inlet duct with a screen covered inlet opening was mounted on one side of the radiator. In crop conditions with a large quantity of light fluffy crop material, the fixed screen would become plugged. These screens were cleaned manually with the internal combustion engine stopped.
Most agricultural harvesters currently manufactured have a screen which rotates. Many of these screens rotate at a relatively high speed and rely on centrifugal force to throw crop material off the screen surface. With these screens, the crop material can slide along the surface of the screen and eventually wear away the metal. Some crop material is so light that it is not removed by centrifugal force. This light material will plug rotating screens. Rotating screens have been modified by the addition of baffles to block the passage of air or by the addition of suckers to suck light material off the screen.
Cyclone separators have also been tried to remove trash from air before the air passes through heat exchangers. Cyclone separators work well in most conditions. However, when there is a substantial amount of very light material that cannot be separated by centrifugal force in the cyclone separator, the heat exchangers can plug.
There is a substantial air pressure drop with both rotating screens and with cyclone separators. To overcome the pressure drop it is necessary to use a relatively large fan or increased fan speed to move air through the screen and the heat exchanger. The relatively large fan or the increased fan speed requires additional power.